<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <script>
        let qy = prompt("请输入你的汽油92/97")
        let zj 
        if(qy==92){
            let num = prompt("请输入几升")
            if(num>=20){
                zj = num * 5.9
            }else {
                zj = num * 6
            }
            alert(zj)
        }else if(qy==97){
            let num = prompt("请输入几升")
            if(num>=20){
                zj = num * 6.5
            }else {
                zj = num * 7
            }
            alert(zj)
        }else{
            alert("没有")
        }
    </script>
</body>
</html>